The present invention is directed to a composition for effecting bone repair. More specifically, the present invention is directed to a moldable composition suitable for implantation to effect bone repair which possesses a certain degree of workability or moldability upon being wetted.
Effecting rapid, suitable repair of large bone defects caused by wounds, surgery, etc. has been a long-standing goal in the orthopedic field. One approach to effecting this repair has been implantation into bone defects of various matter which ultimately becomes an integral part of the healed bone structure, such implants being termed bone graft material. For example, U.S. Pat. No. 4,619,655 is directed to use of plaster of paris (calcium sulfate hemihydrate) as a bioresorbable scaffold for implants and bone repair, notably as scaffolding for incorporating nonresorbable particles such as hydroxyapatite into regenerated bone tissue. Collagen-based bone repair preparations including various particles such as hydroxyapatite are disclosed in U.S. Pat. Nos. 4,888,366; 4,776,890; 4,472,840; 4,563,350; 4,485,097; and 4,678,470.
The physical characteristics of such bone graft material greatly affect the handling and working thereof and also the grafting provided thereby. For example, plaster of paris will tend to lose its workability and set hard within five to ten minutes after mixing with water, making it difficult to mold over an extended period of time to properly fit within a bone defect. Additionally, plaster of paris can take over one month to be resorbed after implantation into a bone defect, which limits the rate at which bone-forming cells can take the place left by resorbed plaster of paris. Collagen tends to possess low viscosity and does not readily form a workable or moldable composition that can be appropriately shaped for implantation into bone.
Furthermore, sustained release of an active ingredient such as a medicament, therapeutic agent or drug has also been a long-pursued goal in the medical field. A sustained release composition which could be implanted within a bone defect such as a surgical or wound site and then release active ingredient over an extended period of time would be of great benefit towards effecting osteogenic healing. Precise control of resorption of a carrier in a sustained release delivery system has been difficult to attain because it has been difficult to control resorption of a matrix or carrier for the active ingredient upon implantation and after a wound or surgical opening has been closed.